n Ergonomics SA : Journal of the Ergonomics Society of South Africa - The effects of different types of cognitive tasks in conjunction with circadian regulation on heart rate variability and performance parameters

Abstract

This study aimed to determine to which extent heart rate variability (HRV) is sensitive to changes in different forms of cognitive workload. The second objective was to determine the effects of cognitive tasks on HRV during different times of the day, in conjunction with the variability of performance parameters. Five tasks were utilized, each at two levels of difficulty in order to ascertain specific cognitive resources. These tasks included a reading task, a decision-making task, a memory task and two forms of modified Fitts tasks. Only one of the modified Fitts tasks, which isolated motor organisation and the spelling error parameter for the difficult reading task showed a time of day effect with respect to performance. With respect to HRV, time domain analysis (rMSSD) and the low frequency (LF) band of a frequency domain analysis showed an overall significant effect of difficulty over all five tasks. The LF band, the high frequency (HF) band, rMSSD and heart rate frequency were sensitive to changes in cognitive workload for the memory task. The LF band was also sensitive to changes in cognitive workload for the modified Fitts task, which isolated motor organisation. The LF-HF ratio was the only HRV parameter that was influenced by the time of day during cognitive task performance. In conclusion, in some instances, HRV was sensitive to changes in cognitive workload for specific HRV parameters and tasks, with selected HRV variables also being affected by time of day. However, no straightforward assignment of workload to HRV parameters and vice versa can be made yet.